As a thin film for filling a contact hole or line or for forming a device or structure in a semiconductor integrated circuit device, silicon, for example, amorphous silicon has been used. In a conventional method, an amorphous silicon film is formed by thermally decomposing monosilane at a temperature of 400 to 600 degrees C. Alternatively, an amorphous silicon film is formed by decomposing disilane at a temperature of 400 to 500 degrees C., decomposing trisilane at a temperature of 350 to 450 degrees C., or decomposing tetrasilane at a temperature of 300 to 400 degrees C.
However, if a contact hole or line being more miniaturized is filled with amorphous silicon, the film formed of amorphous silicon has poor coverage in the contact hole portion, which results in large voids. If the large voids are generated in the contact hole or line, they are one of the factors causing, for example, an increase in resistance. They also deteriorate the accuracy of surface roughness of the amorphous silicon film.
Therefore, in order to improve the accuracy of surface roughness of an amorphous silicon film, a method of forming an amorphous silicon film, in which before an amorphous silicon film is formed, an aminosilane-based gas is supplied on a base surface and a seed layer is previously formed on the base surface, has been proposed.
However, in addition to a need for improvement of surface roughness accuracy of a silicon film, for example, an amorphous silicon film, there is also an increasing requirement for further film thinning, which poses more significant problems.
According to the above conventional art, it may be possible to achieve the object of improving the surface roughness accuracy. However, since further film thinning is required, pinholes are easily formed approximately in 2 nm order and thus it is difficult to thin a film in not more than 2 nm order.